Correspondence Berry pseudorotation

Fig. 55. Schematic progress along a Berry pseudorotation coordinate, with corresponding molecular structures and N-Si-N and O-Si-O angles (degrees).83 Reproduced with permission...

FeC C 0)4 ( C 0). It was found that irradiation of the matrix with the output of a tunable IR laser at a frequency corresponding to one particular isotopomer promoted a selective rearrangement as shown in Scheme 2. These interconversions may clearly be described as pseudorotations but the results show that the permutational mode is not that expected for the normal Berry Pseudorotation seen, for example, in the thermal rearrangement of SF4. Thus the isomerization of Fe(CO)4 was the first reported example of a non-Berry pseudorotation. 

Berry pseudorotation A process of geometrical rearrangement of a five-coordinate complex that transforms a trigonal bipyramid into a pseudo-rotated trigonal bipyramid through a square pyramidal intermediate. It corresponds to the minimal distortion path for the interconversion of trigonal bipyramid and the square pyramid. 

Consider, for example, the molecule PF5 XXXI for which detailed data on the force field are available. Deformations of the valence angle of the equatorial bonds Fj—P—F2 distort this structure to a square-pyramidal structure XXXII, which corresponds to a reaction path calculated [86] for the well-known polytopal rearrangement, the Berry pseudorotation. A stretching of the axial bond P—F4 leads, when calculating by means of Eq. (1.30), to a tetrahedral structure PF4 XXXIII, which parallels the scheme of a SN2-type reaction, while... 

The conformations of four independent cations of the compound 86 correspond to different points on the Berry pseudorotation pathway (Scheme 22) [221]. The percentage of square planar character varies between 19% and 40%. 

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